Vulnerability to infrared seeking missiles currently constitute a serious threat to military aircraft. The aircraft is most vulnerable to attack from surface-to-air and air-to-air infrared guided missiles during takeoff and landing when the infrared emissions from the aircraft are highest.
Past methods used to reduce infrared emissions from aircraft engines have included low-emissivity coatings, shielding of heat emitting surfaces, blocking of the jet exhaust by use of a centerbody air-cooled plenum, injecting various coolants into the engine combustion chambers and using engine fan bypass air to cool tail pipe surfaces. These solutions have all proved unsatisfactory for a variety of reasons.
Low emissivity coatings on jet aircraft engines have limited capability to reduce IR emissions and have been shown to have limited durability. The high temperatures generated on the tail pipe surfaces of a jet engine can quickly degrade the performance of a low emissivity coating and limit its effective operating characteristics. The shielding of heat emitting surfaces of an aircraft engine has proved to be unsatisfactory because the additional weight added to the aircraft engine limits aircraft payload. Also shielding is aerodynamically unsuitable for some types of high performance aircraft. The use of blocking methods causes serious degradation in engine performance due to the increased tail-pipe back pressure. The use of coolants within the jet engine combustion chamber requires the use of excessive quantities of water, therefore reducing aircraft payload and engine performance. Finally, the use of engine fan bypass air reduces the performance of the jet engine as a function of the percentage of bypass air directed at the tail-pipe surfaces. None of these methods, used alone or in combination, were able to provide adequate protection from infrared guided missile systems.
Current infrared countermeasure systems include the use of pyrotechnics and infrared jamming systems. Pyrotechnics consist of flares or other high-heat source projectiles that are ejected from the aircraft in an attempt to mask the infrared emissions of the aircraft engine. Pyrotechnics are not routinely available because they may not always be dispensed during the critical takeoff and landing periods due to their adverse impact on the environment and their potential hazardous effects on populated areas.
Infrared jamming systems while effective are costly and may significantly impact aircraft performance due to the weight and input power requirements of the system. These factors are particularly important for large aircraft during takeoff and landing operations when degraded engine performance cannot be tolerated and engine infrared emissivity is highest.
Therefore, a need has arisen for an apparatus and method that significantly reduces infrared emissivity of the tail-pipe surfaces of a jet engine and has limited impact on engine performance.